Loop through twig array in Drupal

I'm having trouble looping through what I'm hoping is a simple data array in an html.twig file in Drupal 8. When I add the below block to a page, Drupal encounters an "unexpected error". And for now it's okay that this is static to the page.

Note: I'm less than a week into Drupal and twig and my PHP is 10 years rusty.